This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-17018 filed on Jan. 26, 2000.
1. Field of the Invention
The present invention relates to an electromagnetic valve for controlling the pressure of a fluid.
2. Description of the Related Art
Conventionally, as an electromagnetic valve for controlling the pressure of a fluid in response to an electric signal, a spool valve type electromagnetic valve including a spool valve is known. As an example of such a spool valve type electromagnetic valve, there is a pressure adjusting valve disclosed in JP-A-9-166238 and JP-A-10-231946.
In the pressure adjusting valves disclosed in JP-A-9-166238 and JP-A-10-231946, a valve sleeve includes a supply port, an output port and a discharge port. A spool valve axially slides in the valve sleeve. An attracting force of an electromagnet, a spring force and an output pressure feedback force act on the spool valve, and these forces are balanced. By this, the supply pressure of a fluid supplied to the supply port is adjusted to an output pressure corresponding to an input electric signal into an electromagnet portion when this fluid flows out of the output port.
Here, according to the pressure adjusting valve disclosed in JP-A-9-166238, for example as shown in FIG. 4, a pressure adjusting valve 9 includes a sleeve 7 and a spool 8 slidable in an axial direction in the sleeve 7. In the sleeve 7, a discharge port 1 communicating with a slide hole 5 and opening in the outer periphery of the sleeve 7, an output port 2, a supply port 3, and a feedback port 4 are arranged in this sequence from the side of a driving portion 10 for the sleeve 7. A feedback chamber 6 is formed at a front side of the pressure adjusting valve 9 so as to communicate with the feedback port 4.
According to the pressure adjusting valve disclosed in JP-A-10-231946, for example as shown in FIG. 5, a spool valve 109 is attached to a front end face of a linear solenoid 101, and the spool valve 109 accommodates a spool 103 slidably in a sleeve 102. In the sleeve 102, a drain port 104, an output port 105, an input port 106, and a feedback port 107 are formed in sequence from the rear side. A feedback chamber 108 is provided at a front side end portion of the spool 103 so as to communicate with the feedback port 107.
However, in the conventional electromagnetic valves shown in FIGS. 4 and 5, since the output ports 2 and 105 are formed in the radial directions of the sleeves 7 and 10, it is necessary to arrange the electromagnetic valve in parallel with a control valve. Thus, the system becomes large and it becomes difficult to attain a mounting space.
In the electromagnetic valve shown in FIG. 4, the feedback chamber 6 is formed at the front side of the pressure adjusting valve 9, and the spool 8 has a large diameter at the rear side thereof, and has a small diameter at the front side thereof. Thus, when the electromagnetic valve is attached, it is necessary to attach the pressure adjusting valve 9 to the driving portion 10 after the spool 8 is installed into the sleeve 7. The spool 8 has to be frontwardly installed and the pressure adjusting valve 9 has to be rearwardly attached. That is, unidirectional assembling is impossible, thereby increasing the number of fitting steps.
In the electromagnetic valve shown in FIG. 5, since the feedback chamber 108 is formed at the front side end of the spool 103, the spool 103 has to have a small diameter over the whole length. Thus, it is necessary to form a precise hole with a small diameter in the axial direction of the sleeve 102, and the axial length thereof is long with respect to the hole diameter, so that it is difficult to attain a working accuracy.
A first object of the present invention is to provide an electromagnetic valve by which a system is small and it is easy to attain a mounting space.
A second object of the present invention is to provide an electromagnetic valve in which the number of assembling steps is decreased, and assembling accuracy is improved.
According to a first aspect of the present invention, a sleeve includes a first fluid passage passing through a cylindrical peripheral wall, and a second fluid passage opening and formed at an axial end of the sleeve. A magnetic driving portion is fixed to the sleeve at a side opposite to an opening end of the second fluid passage, and generating a driving force. A movable member is slidably supported by an inner wall of the sleeve and receives a magnetic attracting force of the magnetic driving portion, and the movable member includes a third fluid passage communicating with the first and the second fluid passages and reciprocates to switch a communication of the first fluid passage. An urging means for urges the movable member against the magnetic attraction force, and the means is accommodated inside the sleeve.
By making the second fluid passage an output port, the output port is arranged at the side opposite to the magnetic driving portion. Thus, since an electromagnetic valve is arranged in series with a control valve as a control object, a system becomes small, and it becomes easy to attain a mounting space.
According to a second aspect of the present invention, a feedback chamber is formed in the sleeve in a vicinity of the magnetic driving portion and communicates with the first fluid passage. The electromagnetic valve regulates a position of the movable member by a force received from a feedback pressure in the feedback chamber.
By this, the movable member has a small diameter at a side of the magnetic driving portion, and has a large diameter at a side opposite to the magnetic driving portion. Thus, the movable member is installed after the sleeve is attached to the magnetic driving portion. Thus, unidirectional attachment becomes possible and the number of assembling steps is decreased.
According to a third aspect of the present invention, the movable member includes a small-diameter portion slidably supported by the inner wall of the sleeve at a side of the magnetic driving portion. Thus, it is possible to locate a small-diameter hole formed in the sleeve to one place at the side of the magnetic driving portion. Thus, forming the small-diameter hole in the sleeve becomes easy, and forming accuracy is improved, thereby improving the accuracy of oil pressure control.